1. Field of the Invention
The present invention relates to a spatial light modulator for spatially modulating incident light.
2. Description of the Related Art
A spatial light modulator for spatially modulating incident light is used in the field of an optical information processing, a computer-generated hologram or the like.
A conventional spatial light modulator includes one using a liquid crystal and one using a micro-mirror device.
In the foregoing field of the optical information processing, the computer-generated hologram or the like, since a large amount of information must be processed at high speed, it is desirable that the spatial light modulator has a high operation speed.
However, the spatial light modulator using a liquid crystal has a problem that the operation speed is low. For example, even in the spatial light modulator using a ferroelectric liquid crystal that has a high operation speed among liquid crystals, the response time is of the order of microsecond.
The spatial light modulator using a micro-mirror device can operate at a relatively high speed. However, since this spatial light modulator is a micro machine manufactured by a highly-developed semiconductor manufacturing process and having a complicated structure, the manufacturing cost is high, and there remains a problem in reliability since it has a mechanical driving portion.
Now, for example, U.S. Pat. No. 4,584,237, No. 5,241,421, No. 5,255,119 and No. 5,386,313 disclose spatial light modulators utilizing a magneto-optic effect. Hereinafter, such a spatial light modulator is referred to as a magneto-optic spatial light modulator. The magneto-optic spatial light modulator includes a plurality of pixels each of which is made of a magneto-optic material and can independently select the magnetization direction. In the magneto-optic spatial light modulator, the polarization direction of light passing through each pixel is rotated by a predetermined angle in a direction opposite to a magnetization direction in each pixel in accordance with the Faraday effect. Accordingly, the magneto-optic spatial light modulator produces spatially modulated light by arbitrarily selecting the magnetization direction in each pixel.
In the conventional magneto-optic spatial light modulator, two kinds of conductors are provided in a grid form to intersect with each other at a position of each pixel. When magnetization in any one of the pixels is to be reversed, a current is passed through two conductors intersecting with each other at the position of the pixel, so that a magnetic field for reversing the magnetization in the pixel is produced.
In the foregoing conventional magneto-optic spatial light modulator, the polarization direction of passing light is rotated by using only a magnetic layer made up of a single layer of a magneto-optic material. Thus, in this magneto-optic spatial light modulator, in order to enhance the Faraday effect to improve magneto-optic performance, it is necessary to increase the thickness of the magnetic layer.
However, the magnetic field obtained by passing a current through the conductor decreases inversely with the square of a distance from the conductor. Thus, if the thickness of the magnetic layer is increased, it is necessary to increase the value of the current to be passed through the conductor to reverse the magnetization in each pixel, and as a result, power consumption becomes high. Besides, if the thickness of the magnetic layer is increased, the reversal speed of magnetization in the pixel, that is, the operation speed of the magneto-optic spatial light modulator, is lowered.
Besides, in the conventional magneto-optic spatial light modulator, the plurality of pixels are separated from one another by, for example, grid-like grooves formed in the magnetic layer. In such a magneto-optic spatial light modulator, if the thickness of the magnetic layer is increased, it becomes necessary to increase the depths of the grooves formed in the magnetic layer as well, and therefore it becomes difficult to form the grooves. Further, if the depths of the grooves are increased, it becomes impossible to directly form the conductor on the magnetic layer. Thus, it becomes necessary that each groove is filled with an insulating material, the top surface of the magnetic layer is flattened, and then, the conductor is formed on the magnetic layer. In addition, if the depths of the grooves are increased, it becomes technically difficult to fill the grooves with the insulating material and to flatten the top surface of the magnetic layer.